Non-melanoma skin cancers, of which 80 percent are basal cell carcinomas (BCC), are the most common cancers in the US, with more than one million diagnoses annually. Data suggest increasing incidence of BCC tumors of the torso and in young women. In comparison to most other malignancies, thorough descriptive and analytic epidemiologic data are markedly deficient. Although early-onset cancers may be more genetically driven, this rapid increase suggests an environmental cause (in a genetically susceptible population) which has not yet been identified. There is also a need to evaluate the validity of self-reported ultraviolet (UV) radiation exposure, used in most epidemiologic studies of skin cancer, in relation to objective tissue/tumor biomarkers. I will focus on three research areas (1) assessing how self-reported measures of UV correlate with more objective measures of skin damage (solar elastosis) and molecular level tumor mutations; (2) investigating environmental/lifestyle factors (UV exposure, tanning bed use, and caffeine intake) in relation to BCC; and (3) describing and evaluating indoor and outdoor tanning behaviors ,attitudes, and knowledge to identify potential barriers to sun protection and sunless tanning. All analyses will be conducted in the Yale SPORE for Skin Cancer case-control study with a targeted enrollment of 500 newly diagnosed BCC cases and 500 controls (benign lesions) < 40 years of age. Participants complete an in- person interview based on a structured questionnaire, which elicits information on sociodemographic and anthropometric factors, solar/other radiation, sunless tanning, tobacco and alcohol, personal/family history of cancer, oral contraceptive use, and caffeine intake. I will calculate percent agreement, Kappa statistics, and Pearson correlation coefficients to compare self-reported measures to tissue/tumor biomarkers. To identifying risk factors, I will use unconditional logistic regression to estimate odds ratios and 95% confidence intervals for the independent association of the factors of interest on BCC. Finally, I will describe common attitudes, behaviors, and knowledge regarding tanning and sunless tanning in the study population and identify sociodemographic and clinical correlates. BCC is one of the most common cancers, so identifying new risk factors in an epidemiologic study can have a significant, but low-cost impact on primary prevention. Although BCC is treatable, individuals incur significant healthcare costs and decreased quality of life. With this research, I can assess the validity of epidemiologic measures of UV, evaluate new exposures that might explain the recent increase in BCC in younger individuals, and with comprehensive data on tanning attitudes, behaviors, and knowledge, my findings can be translated into preventive interventions.